Petrol gauge problem

[Charles Levien]

I fitted new sender unit fairly recently and gauge was working but without giving a steady reading. I loosened gauge and found that in certain positions it would read accurately without flickering but on re tightening the problem returned so I assumed it was a faulty earth. So I fished the gauge out again and noticed a blob of solder near the rim, at the back. Presuming this to be where an earth wire was originally attached I soldered another on and connected the wire directly to battery earth. 
The gauge is now dead — question, have I damaged the gauge by heating up that little blob of solder on the back? Am I now looking for another gauge?

Charles